At present, no data exist on the value of long-term preventative lithium therapy in adolescents with bipolar affective illness (BPI). The main objective of this collaborative, multicenter proposal is to conduct a five-year double-blind placebo controlled study of lithium discontinuation in adolescents with BPI. The participating institutions include UCLA (Michael Strober, PI), University of Pittsburgh (Neal Ryan, PI), and Brown University (Martin Keller, PI). Each site will recruit 10 patients per year who fulfill DSM-III-R criteria for BPI. Subjects who will be eligible for enrollment into this discontinuation protocol are adolescents from Tanner stage III to 19 years, 11 months who have been stabilized on lithium for a period of at least 6 months and who have been asymptomatic on lithium without any other psychoactive medication for at least 3 months. Specific aims are: (1) to compare the efficacy of lithium vs placebo in preventing recurrences of either mania or depression, and in controlling subsyndromic symptoms and onset of nonaffective psychiatric disturbances; (2) to identify predictors of differential outcome within and across treatment cells; and (3) to assess emergent side effects and overall compliance with lithium maintenance during the study period. We believe that this study-the first of its kind, to our knowledge-will add significant new clinical and theoretical knowledge to the emerging literature on pediatric psychopharmacology.